Polycarbonate resins (hereinafter also referred to as “PC resin”) made of 2,2-bis(4-hydroxyphenyl) propane (commonly known as bisphenol A) exhibit high transparency and excellent mechanical characteristics. Such polycarbonate resins have been conventionally put into various uses such as use in optical materials and use in electronic materials. However, as PC resins are put in more increasing use, more advanced performance has been demanded on PC resins. PC resins having more excellent performance are being demanded. For instance, PC resins for use in electrophotographic photoreceptors are demanded to have not only higher mechanical characteristics but also higher transparency, more stable electrostatic characteristics so as to be more invulnerable to repeated cycle of electrification and neutralization or more favorable solubility in non-halogen solvents.
For such demands, a Patent Document 1, for example, discloses a method of obtaining a polycarbonate copolymer (hereinafter also referred to as “copolymerized PC”) capable of exerting excellent heat resistance without deterioration in transparency by performing polycondensation with use of a material in which a bisphenol A and a specific bisphenol are mixed as phenol structural unit. In addition, a technique for applying such copolymers to electrophotographic photoreceptors is also known (e.g., Patent Document 2).
Other examples of known techniques are a technique for obtaining a polycarbonate copolymer having YI of approximately 1.3 to 1.4 (e.g., Patent Document 3) and a technique for obtaining polycarbonate having low yellow index (YI) by controlling an amount of oxygen dissolved in a sodium bisphenolate solution to be less than 150 ppb (e.g., Patent Document 4).
A further example of known methods is a method of obtaining a polycarbonate copolymer having favorable hue by using fluorene-base bisphenol under substantially no presence of oxygen (e.g., Patent Document 5).
Patent Document 1: Japanese Patent No. 1965051
Patent Document 2: Japanese Patent No. 2531852
Patent Document 3: JP-A-5-117382
Patent Document 4: JP-T-2002-533544
Patent Document 5: JP-A-2005-82677